Membrane cover having a protective layer to prevent deterioration of UV stabilizers therein
The membrane structure according to the present invention has a top layer containing three plies. The top ply has UV stabilizers embedded therein; the bottom ply has stretch-resistant elements embedded therein; and the middle ply contains a co-extruded polyvinylidene chloride barrier film for example, for protecting the top ply against bio-gas infiltrations therein. In another aspect, the top and bottom plies containing polyethylene for protecting the middle ply from the weather and from corrosive environments under the membrane cover. In yet another aspect, the membrane structure has two foam layers affixed to the bottom ply. Each foam layer is made of juxtaposed strips of semi-rigid, closed-cell, polyethylene foam; wherein each strip in one foam layer is laid astride the adjoining edges of a pair of strips in the other foam layer. The strips of foam are bonded together and to the undersurface of the bottom ply by strips of fused polyethylene.
1 . A structure of a floating membrane cover for covering a wastewater reservoir, comprising;
a top ply having UV stabilizers embedded therein and a first impermeability to bio-gases; and
a bio-gas shield laid beneath said top ply for preventing a migration of bio-gases into said top ply and a deterioration of said UV stabilizers in said top ply; said bio-gas shield having a second impermeability to bio-gases, and said second impermeability to bio-gases having a greater extent than said first impermeability of said top ply.
2 . The structure as claimed in claim 1 , further comprising a structural ply laid beneath said bio-gas shield and having said first impermeability to bio-gases and stretch-resistant elements embedded therein.
3 . The structure as claimed in claim 1 , wherein said bio-gas shield contains a co-extruded polyvinylidene chloride barrier film.
4 . The structure as claimed in claim 2 , wherein second impermeability to bio-gases has a greater extent than said first impermeability by a factor of two.
5 . The structure as claimed in claim 2 , wherein said top ply, said bio-gas shield and said structural ply contain polyethylene and are bonded together.
6 . The structure as claimed in claim 2 , further comprising a first and second foam layers affixed to said structural ply.
7 . The structure as claimed in claim 6 , wherein said first and second foam layers are made of polyethylene and are bonded together by strips of fused polyethylene.
8 . The structure as claimed in claim 2 wherein said stretch-resistant element is a high-strength fabric.
9 . The structure as claimed in claim 7 , wherein said first foam layer is bonded to said structural layer by strips of fused polyethylene.
10 . A method of constructing a membrane cover with enhanced resistance to UV radiations, comprising the steps of:
constructing said membrane cover with three plies including a top ply containing UV stabilizers embedded therein; a bottom ply containing reinforcing elements embedded therein; and a middle ply laid between said top ply and said bottom ply;
selecting a material of construction of said middle ply such that said middle ply is more impermeable to bio-gases than said bottom ply, for restricting a passage of bio-gases there through and for reducing corrosion of said UV stabilizers.
11 . The method as claimed in claim 10 further including the step of selecting a material of fabrication of said top ply and said bottom ply, containing polyethylene, for protecting said middle ply from weather conditions and from corrosive environments.
12 . The method as claimed in claim 11 , wherein said step of selecting a material of construction of said middle ply comprises the step of selecting a material of construction that is at least twice as more impermeable to bio-gases than said bottom ply.
13 . The method as claimed in claim 12 , further including the step of bonding to an undersurface of said bottom ply, a first foam layer made of a closed-cell rigid polyethylene foam, having a thickness of about one-half inch.
14 . The method as claimed in claim 13 , further including the step of bonding to an undersurface of said first foam layer, a second polyethylene foam layer also having a thickness of about one-half inch.
15 . A structure of a membrane cover for covering a wastewater reservoir, comprising;
a top layer made a stretch-resistant polyethylene-based pliable sheet material;
a middle foam layer bonded to an undersurface of said top layer; and
a lower foam layer bonded to an undersurface of said middle foam layer;
each of said foam layers being made of juxtaposed strips of semi-rigid, closed-cell, polyethylene foam; and each strip in one of said foam layers being laid astride adjoining edges in a pair of strips in said other foam layer.
16 . The structure as claimed in claim 15 , wherein said lower layer is bonded to said middle layer; and said middle layer is bonded to said top layer, by localized strips of fused polyethylene.
17 . The structure as claimed in claim 16 wherein said each of said foam layers has a thickness of about one-half inch.
18 . The structure as claimed in claim 16 wherein said top layer has three plies including a top ply having UV stabilizers embedded therein, a structural ply having stretch-resistant elements embedded therein and a bio-gas shield laid between said top ply and said structural ply.
19 The structure as claimed in claim 18 , wherein said bio-gas shield has an impermeability to bio-gas that is greater than an impermeability to bio-gases of said structural ply.
20 . The structure as claimed in claim 19 , wherein said bio-gas shield has an impermeability to bio-gas that is greater than an impermeability to bio-gases of said structural ply by a factor of two.